Measurement of pulmonary tissue volume and blood flow in persons with normal and edematous lungs

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Abstract
Pulmonary tissue volume (Vt) and pulmonary capillary blood flow (.ovrhdot.Qc) were measured by a rebreathing method using 2 soluble gases, acetylene (C2H2) and dimethyl ether (DME), in 32 normal subjects and 14 patients who had pulmonary edema. In 18 of the normal subjects, studies were performed at 3 or more different rebreathing volumes (VA). To normalize for differences in body size, results were expressed as the ratio of Vt or VA to predicted total lung capacity (TLC). Changes in VA/TLC had a significant effect on Vt/TLC and .ovrhdot.Qc measured with both gases. The range of normal values for Vt was best defined by expressing the relationship between Vt/TLC and VA/TLC. Using this approach, many patients with clinically mild or inapparent pulmonary edema had abnormal values of Vt. When comparing mean values of C2H2 and DME in 82 simultaneous measurements at constant VA/TLC, Vt was significantly higher in 87% (71/82) and .ovrhdot.Qc in 63% (52/82) of the paired tests.